In recent years, in order to meet demands for stylish appearances of TVs and mobile equipment, frame narrowing has been progressed which narrows an outer frame surrounding a display device. Therefore, the shape of a loudspeaker generally installed in a frame is desired to be slimmer.
However, in a slim loudspeaker, since the width thereof in a short side direction is narrowed, a sufficient width of a suspension that holds a diaphragm cannot be secured. Therefore, stiffness of the suspension increases, and a minimum resonant frequency f0 of the loudspeaker also increases. As a result, low-frequency characteristics are degraded, and reproduction frequency bandwidth is reduced. As a countermeasure to this problem, Patent Literature 1 proposes a conventional loudspeaker which is a slim loudspeaker utilizing a magnetic fluid and separated suspensions and in which reproduction frequency bandwidth is not reduced.
FIG. 22(a) is a diagram showing a cross-sectional view of a loudspeaker 600 using a magnetic fluid and separated suspensions, which is the conventional loudspeaker disclosed in Patent Literature 1. FIG. 22(b) is a cross-sectional view of the loudspeaker 600 taken along a line A-B in FIG. 22(a) and viewed in a direction of an arrow C. The loudspeaker 600 includes a yoke 601, a magnet 602, a plate 603, a diaphragm 604, suspensions 605a and 605b, a voice coil 606, a sound hole 608, ribs 609, and a magnetic fluid 610. The magnet 602, whose front outer shape is a track shape, is bonded to an inner bottom surface of the box-shaped yoke 601 with an upper surface being opened. The plate 603, whose front outer shape is a track shape, is bonded to an upper surface of the magnet 602. A magnetic gap 607 is formed between the yoke 601 and the plate 603. Thus, the yoke 601, the magnet 602, and the plate 603 form a magnetic circuit having the magnetic gap 607. The sound hole 608 is formed penetrating through the yoke 601, the magnet 602, and the plate 603 along a central axis O. The diaphragm 604 is formed with a plurality of ribs 609 parallel to the short sides of the diaphragm 604. The suspensions 605a and 605b are provided on the short sides of the diaphragm 604, as a support that vibratably supports the diaphragm 604. That is, a suspension is not provided surrounding the entire circumference of the diaphragm 604, but a plurality of independent suspensions (separated suspensions) are provided on portions of the diaphragm 604. The suspensions 605a and 605b are made of the same material as that of the diaphragm 604, and are formed integrally with the diaphragm 604. The voice coil 606, whose front outer shape and front inner shape are track shapes, is provided in the magnetic gap 607. In addition to the voice coil 606, the magnetic fluid 610 is filled in the magnetic gap 607. In the conventional loudspeaker 600 disclosed in Patent Literature 1, the magnetic fluid 610 is filled only on an inner circumference side of the voice coil 606 in the magnetic gap 607.
According to the above configuration, the suspensions 605a and 605b that vibratably support the diaphragm 604 are provided at the different positions on the outer circumference of the diaphragm 604. Therefore, even when the loudspeaker is reduced in size, the stiffness can be reduced by adjusting the width and thickness of the suspensions 605a and 605b, and thus the minimum resonance frequency can be reduced. Further, since the magnetic gap 607 is filled with the magnetic fluid 610, interference between sound waves which occurs at the surfaces of the diaphragm 604, and rolling can be suppressed. As described above, by using the loudspeaker 600 that utilizes the magnetic fluid 610 and the separated suspensions 605a and 605b, it is possible to suppress reduction in the reproduction frequency bandwidth that is a problem in a slim loudspeaker.